Aquatic Invasive Species

Most invasive species pose no direct threat to and have no immediate impact on human life; however, since its introduction in the 1940s, Eurasian watermilfoil (Myriophyllum spicatum) has wreaked havoc on inland bodies of water throughout the United States.  The species has already invaded forty-four of the fifty states and its rapid proliferation causes swimming, boating, and fishing problems.

A proposed study at Duke University is seeking funding in order to investigate novel approaches to control of Eurasian watermilfoil.  Because previous studies have already shown that Eurasian watermilfoil is susceptible to biological control via the milfoil weevil (Euhrychiopsis lecontei), the aim of the proposed study is to use this weakness to find other methods to control the invading watermilfoil.

The study, suggested by Duke undergraduate Emily Chang, focuses on the relationship between the Eurasian watermilfoil and the E. lecontei weevils.  The weevils have been used to control the invading plant in other areas because they chew through the plant’s tissues, which results in the collapse, and death, of the plant.  The proposed study looks to analyze the composition of the plants in terms of chemical elements, organic functional groups, and damaged nonstructural hydrocarbons after the weevils have invaded a population of Eurasian watermilfoil.  Chang hopes that this information will provide insight into “the chemical nature of this biocontrol method” and will “allow scientists to improve the effects of biocontrol by manipulating the chemistry operating behind the watermilfoil.”

Chang states that “if milfoil can spread as much as it has, it is clearly very powerful and has the potential to spread everywhere.”  Thus, in hopes to combat the spread of this invasive species, Chang has proposed a study that hopes to advocate the use of biocontrol as a stepping block for the expansion of chemical control.  Currently, Chang feels that biocontrol is the only feasible method of dealing with Eurasian watermilfoil and notes that “mechanical control is bad because it is time consuming because each plant must be hand plucked and because milfoil is a resilient species.  Chemical control is also a poor option because it only offers temporary relief.”  However, Chang hopes to change this by using information from biological control to foster the development of chemical controls that will cause permanent effects.

Chang’s experiment will utilize four lakes that have substantial Eurasian watermilfoil populations.  Four 3×5 meter plots will be created for analysis; one plot will be a control containing just the watermilfoil, and the other three plots will contain the watermilfoil with varying numbers of weevil population densities.  The different plots will be monitored from May to October for three consecutives years.  Once a month, fifteen plants will be removed from each plot, frozen, then dried and crushed and analyzed for carbohydrate concentration.  Some methods of elemental analysis include the use of a CHN Analyzer, infrared spectroscopy (IR), and nuclear magnetic resonance spectroscopy (NMR).  The plant samples will be compared to the original composition of watermilfoil before the study.  On a side note, the contents of the weevils’ stomachs will also be analyzed in order to determine which tissues are targeted in feeding.

If specific carbohydrates are targeted by the milfoil weevils, the future of control could be very optimistic.  Scientists would be able to focus on attacking the specific weak carbohydrates and functional groups in order to take down the invading Eurasian watermilfoil populations.  Chang hopes to use chemical control to help thwart the dangers of watermilfoil and concludes that “if we can pinpoint which carbohydrates are favored, … we can apply certain chemical herbicides to cause plants to die and disappear.”

Emily Chang

Professor Sandra Cooke

Writing 20

24 March 2010

To Decline, or Not to Decline?

J. Aquat. Plant Manage 38: 105-111 (2000)

A study by Raymond M. Newman and David D. Biesboer (2000), both of the University of Minnesota, investigates whether there are possible relationships between the population of the milfoil weevil Euhrychiopsis lecontei and that of Eurasian watermilfoil (Myriophyllum spicatum). Control of the aquatic milfoil plant is important because it has harmed aquatic diversity, hindered human boating and recreation, and withstood both mechanical and chemical control methods. The researchers examined the Eurasian watermilfoil colonies and abiotic conditions, such as alkalinity, of the man-made Cenaiko Lake from 1996 to 1998. Samples of milfoil plants were collected from the lake and tested for carbohydrate analysis and weevil density determination after the plants were dried. The results of the study showed that declines in milfoil populations caused increases in the biomass of other plant species. Increases or decreases in weevil populations  paralleled those in watermilfoil. The researchers conclude that larger-scale experiments involving the watermilfoil, weevil, and their environment will help support these findings.

J. Aquat. Plant Manage 38: 78-81 (2000)

A study led by Robert P. Creed, Jr., of Appalachian State University investigates the use of biological control to restrain the spread of Myriophyllum spicatum, better known as the Eurasian watermilfoil. This aquatic plant has invaded lakes across North America, and scientists are examining the effects of the North American weevil (Euhrychiopsis lecontei) on watermilfoil on 4 environmental levels ranging from the individual plant to entire geographic regions. On the smallest scale, that of an individual plant, weevil larvae damage meristems, which hinders stem growth, and both larvae and pupae injure vascular tissue, preventing roots from getting nonstructural carbohydrates. Also, scientists found that weevils can make watermilfoil beds collapse in lakes, but the precise weevil density to cause this is uncertain. More research concerning aquatic predators, the nutrient content in sediment, and the regional climate is necessary. Creed concludes that further investigation is crucial at all four spatial levels to determine the efficacy of weevil biocontrol on watermilfoil.

In 1989, water hyacinth first appeared on Lake Victoria.  Without natural enemies to control its spread, it quickly expanded and became a troublesome invader to the ecosystem.  By 2000, the population had been brought back to a reasonable level, and there are two competing explanations for this decline: weevils and the El Niño weather pattern in 1997-1998.

According to Wilson et al. (2007), the main cause of the hyacinth decline was the introduction of weevils into the area, an insect that feeds on the plant, causing it considerable damage.  The weevils were brought as a means of biocontrol, and Wilson et al. (2007) claim that they weakened the hyacinth, making it more susceptible to the inclement weather, and then finishing off the remaining hyacinth that surged in the aftermath of El Niño.  They specifically cite the fact that the four years it took for the hyacinth population to be fully controlled is consistent with the time frames that occurred in weevil biocontrol of hyacinth in other areas, as well as the fact that the hyacinth population started to flourish again after El Niño, suggesting that the stormy weather alone did not cause its eventual downfall.

Williams et al. (2007), on the other hand, argue that it was in fact the El Niño weather pattern that played the biggest role.  They point to Lake Victoria’s size and diverse range of habitats, claiming that Wilson et al. (2007) oversimplify the true nature of the hyacinth’s decline.  By looking at the data for each section of the lake, Williams et al. (2007) show that nearly all hyacinth not in a sheltered gulf area was eliminated simultaneously in late 1997 to early 1998, the same time as the El Niño event.  They acknowledge that weevils no doubt played a large role in weakening the plants, but assert that Wilson et al. (2007) give too much credit to the success of the biocontrol.

Ultimately, later photos revealed that water hyacinth has returned to Lake Victoria in extreme quantities in the sheltered Winam Gulf area.  I believe that this suggests that Williams et al. were more correct in their analysis of the situation, as it appears that, in the area of Lake Victoria that was protected from the worst of the El Niño weather, the weevils alone were not enough to eliminate the hyacinth in the long term.  Nonetheless, both sides emphasize the fact that the decline was due to a variety of factors, and neither can be considered completely correct, since water hyacinth never was truly eliminated.  On a wider scale, this leads one to wonder how successful any biocontrol effort can ever be, and if perhaps all one can do is forestall the inevitable.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-Invades Lake Victoria.
http://earthobservatory.nasa.gov/IOTD/veiw.php?id=7426. Viewed 27 January 2010

Williams, A.E, R.E Hecky and H.C. Duthie. 2007. Water hyacinth decline across Lake Victoria- Was it caused by climatic perturbation or biological control? A Reply. Aquatic Botany 87:94-96

Wilson, J.R.U., O. Ajuonu, T.D. Center, M.P. Hill, M.H. Julien, F.F. Katagaria, P. Neuenschwander, S.W. Njoka, J. Ogwang, R.H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87: 90-93

Emilia Rybak

Ever since water hyacinth was first reported on Lake Victoria in 1989, this invasive species has wreaked havoc on the lake and the valuable biodiversity that depend on it for survival. Although there is no disagreement regarding how much destruction water hyacinth has caused, there is an ongoing debate concerning the factors that brought about its decline in 1998.

Some scientists agree with the argument presented by Wilson et al. (2007) that wet and cloudy weather patterns caused by El Nino played a vital role in the water hyacinth’s decline in the second half of 1997 and the first half of 1998. However, others believe that, as Williams et al. (2005) argue, that the introduction of Neochetina spp., or weevils, in Lake Victoria as a form of bio-control was responsible for this drop.

Specifically, Wilson et al. state that the four-year gap between when weevils were introduced in Lake Victoria in 1995 and when they started to produce results is consistent with results of other bio-control agents in other countries. Thus, they argue that weevils were primarily accountable for the water hyacinth decline since their effects occurred in accordance with those of other species. On the other hand, Williams et al. assert that prolonged sub-optimal light will reduce growth and reproduction rates of plants while enhancing the results of other debilitating forces, including weevil herbivory. Therefore, the stormy weather in 1998 provided ideal conditions for impeding the spread of water hyacinth, and thus aided the weevils in declining the water hyacinth population.

I think that the argument of Williams et al. is more convincing since it acknowledges that El Nino weather patterns were not solely responsible for causing the decline in water hyacinth, but rather that the combined effects of El Nino and the weevils enabled the decline. Even if the weevil population did only begin to produce results after four years, it is undeniable that the El Nino patterns contributed to their efficacy.

The MODIS satellite images taken in 2005 and 2006 that display the resurgence of water hyacinth on Lake Victoria demonstrate that bio-control is not a fully reliable method of managing invasive species. They show that bio-control may sometimes be an effective strategy, yet its efficacy often falls short. Thus, scientists should not completely depend on this method to eradicate an invasive species, and both invasive species and bio-control agents should be regularly monitored to avoid resurgences.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-Invades Lake Victoria.
http://earthobservatory.nasa.gov/IOTD/veiw.php?id=7426. Viewed 27 January 2010

Williams, A.E, R.E Hecky and H.C. Duthie. 2007. Water hyacinth decline across Lake Victoria- Was it caused by climatic perturbation or biological control? A Reply. Aquatic Botany 87:94-96

Wilson, J.R.U., O. Ajuonu, T.D. Center, M.P. Hill, M.H. Julien, F.F. Katagaria, P. Neuenschwander, S.W. Njoka, J. Ogwang, R.H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87: 90-93

Since its introduction in the late twentieth century, water hyacinth has been a major nuisance in Lake Victoria.  Not only does it pollute the water by disrupting the lake’s flow, but because of the plant’s massive undergrowth, also reduces fishermen’s abilities to make a living and poses as a major threat to native species. To attempt to counteract this invasive species, in 1995, weevils, which are small herbivore beetles and natural predators of water hyacinth, were released into the water hyacinth clusters as biological control agents.

However, according to Williams et al. (2006), though the weevils aided in the reduction of water hyacinth in Lake Victoria from 1999 to 2000, they were not the main reason for the plant’s reduction. Another factor, the El Nino of 1997 – 1998, which had been the biggest ever recorded in the twentieth century, was, according to Williams et al. (2006), the most important contributing factor to the water hyacinth’s decline. Williams et al. (2006) argues that it was because of a combination of timing, reduced sunlight, and weevils, that the decline of water hyacinth in 1999/2000 was so dramatic. Therefore, Williams et al. (2006) warns that now the El Nino has calmed, the water hyacinth will resurge; the weevils will be unable to keep the plant population under control.

Wilson et al. (2006), on the other hand, argues that the weevils were crucial, if not the only factor in the water hyacinth’s decline, and that the El Nino had little effect on the plant’s growth. This is because, according to Wilson et al. (2006), the weevils generally takes three to five years to fully reach their potential and the decline in water hyacinth fits that timeline perfectly in accordance with the three releases of weevil nests into the water hyacinth clusters. The El Nino, on the other hand, though would have moved already weevil-weakened water hyacinth mats around, could not have had reduced water hyacinth growth by increased cloud cover; there is no substantive link between low light and water hyacinth concentration. (Wilson et al., 2006)

In light of all the evidence, I think that Williams et al. (2006) gives a more convincing argument than Wilson et al. (2006), because the latter neglected many sides of the former’s argument, and did not even consider the possibility that water hyacinth might return, even if it weren’t because of the El Nino’s dispersion.

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/vi…. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

Water hyacinth is a fast growing South American plant which spread along the shores of Africa’s Lake Victoria, forming a blanket that suffocated native species and the fish industry.  To combat this plant, weevils were introduced and several years later the water hyacinth population began to decline.  The biologists responsible for this action have claimed victory; however these claims have been challenged by other scientists who point to atypical weather phenomena as playing a role in the water hyacinth’s decline.

Wilson et al.  (2007) argues that the implementation of biological control by introducing the weevils is primarily responsible for the subsequent decline in the water hyacinth.  They support this conclusion with estimates of total water hyacinth coverage of Lake Victoria extrapolated from satellite data that show a marked decline approximately 3 years after the weevils were introduced.  Also, they note that this result is similar to that of other nations who have enacted this form of biological control and that the introduction of weevils is the only management technique common to all parts of the lake.

The argument that weather phenomena, specifically the El Nino event of 1997/1998 contributed significantly to the decline of water hyacinth on Lake Victoria is expressed by Williams et al. (2007).  They maintain that the lake-wide summaries produced by Wilson et al. (2007) do not respect the diversity and size of Lake Victoria.  Thus, they examine each of the lake’s main sections separately and noticed that the water hyacinth began to decline in all three sections roughly simultaneously after the El Nino event whereas the weevils had been introduced to each region at different times.  Their argument therefore is that the El Nino event weakened the water hyacinth population and left it susceptible to destruction by both the weevils and other factors.

I agree with Williams et al. (1997) that the water hyacinth population of Lake Victoria cannot be accurately modeled as a single graph.  The simultaneous decline of water hyacinth suggests a cause that is universal, not susceptible to regional variation like the weevil population.  The importance of regional considerations was recently highlighted by a report from the NASA Earth Observatory (2007) which found that rain runoff had sparked a rapid resurgence of water hyacinth.  Efforts to control this new growth and prevent future growth should place an emphasis on regional attributes such as agriculture that make a region susceptible to water hyacinth invasion.

Eli Wilber

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

When someone plants a water hyacinth to liven up the flora in his garden pond, the idea of initializing the spread of an invasive species is probably not the first thing to come to mind.  Not only does water hyacinth impede Lake Victoria fisherman from doing their jobs, but it also blankets the surface of the lake and prevents underwater aquatic species from getting essential sunlight.  Efforts have been made to mitigate the spread of the water hyacinth, most notably the introduction of the Neochetina weevil to Lake Victoria.  Through these efforts using biocontrol and the effects of El Nino, the water hyacinth population was at a time diminished significantly.  However, the population is only recently starting to once again emerge and thrive in Lake Victoria.

According to Wilson et al. (2007), the decline in the water hyacinth population was primarily due to the Neochetina weevil.  While evidence certainly points to most of the damage to the population being due to the waves caused by El Nino, Wilson et al. (2007) claims that the weevils are what truly kept the hyacinth in check.  The article even goes as far as to say that “the El Nino event may have been a major stress to the plants…[but] the plants were already badly damaged by the weevils” (Wilson et al. (2007)) which just goes to show how the weevils played a major role in water hyacinth reduction.

On the other side of the spectrum, Williams et al. (2007) does not accredit the Neochetina weevil as the chief agent in reducing the water hyacinth in Lake Victoria, but instead the severe weather patterns of El Nino.  Through use of graphs and hard scientific data of hyacinth population through time, Williams et al. (2007) claims that hyacinth population did not actually decline until El Nino caused the waves which uprooted most of the population in Lake Victoria.

While both articles present a clear and convincing reason as to the causation of the water hyacinth population decline, I believe that Wilson et al. (2007) is the more legitimate of the two.  Aside from being a physically longer article, I like Wilson et al. (2007) because it does not beat around the bush in how it admits that the population decline was primarily caused El Nino, but the only reason the damage was possible was because the plants were weakened by weevils prior to El Nino.  Even if El Nino was the main cause for the destruction of the species, it was seen that after the storm the weevil population declined which in turn gave rise to an increase in water hyacinth population.  So in summation, I feel that Wilson et al. (2007) is an overall better article.  Furthermore, if you ever plan on planting  anything, you would be well advised to check if this plant could possibly cause an aquatic invasive epidemic.  If anything, do it for the sake of the weevils.

Sources

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/vi…. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

In recent years, bio-control has become a popular but controversial subject in environmental science fields. Many times, it has not worked out the way scientists predicted and has actually had negative impacts on the very ecosystems that they were trying to help. People first reported water hyacinths on Lake Victoria in 1989. Since then, they have spread exponentially covering tens of thousands of hectares of water surface hampering transportation, fishing, and the lake’s biodiversity.

Wilson et al. explain that in 1995, scientists imported bio-control agents called weevils into the Great Lakes Region to control water hyacinth growth. They continue to discuss that in 1997/1998, there was an El Nino weather pattern in the region, which caused very stormy and wet weather. Wilson et al. believe that the reduction in water hyacinth occurred as a result of the weevils and that there is little chance of a resurgence of water hyacinth. They argue that water hyacinth continued to grow until 1998 then had a small reduction coinciding with the El Nino and then continued to multiply further until 2000. Then, at that point, there was a significant reduction of water hyacinth; they state that this timeline of approximately four years before weevils were effective is similar to that of other bio-control situations elsewhere (2007).

Williams et al. have different ideas; they do not deny that the bio-control helped control water hyacinth growth. However, they maintain that the El Nino greatly accelerated this process by the wet weather and wave action. They state that there was a small growth of water hyacinth in 2000-2001 and believe that it is very likely to see a resurgence soon because weevils were not solely responsible for the decrease in water hyacinth. Furthermore, many weevils were destroyed in the El Nino weather as well (2007).

I believe that both sides present excellent evidence supporting their arguments; however, due to Wilson et al.’s explanation of the typical timeline of biodiversity, I am inclined to believe that they are more convincing than Williams et al. Nevertheless, the recent NASA satellite images clearly depict that the weevils did not have as significant an impact as Williams et al. thought or were unable to perform their intended purpose after El Nino. I think this situation illustrates that bio-control can be helpful, but one must be prepared when implementing this strategy for unexpected results or complications.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/vi…. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H. C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87:94-96.

Wilson, J. R. U., O. Ajuonu, T. D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87:90-93.

Water hyacinth is a marine plant native to South America. Over the last few decades, however, it has infested Lake Victoria and made it hard for local fishermen to maintain their lifestyle. Large mats of water hyacinth have clogged waterways, reduced small local marine life, and blocked sunlight from reaching the lake bottom. Recently, there have been efforts to reduce the water hyacinth population, but whether they have been effective or not is another matter.

Williams et al. (2007) states that the waves caused by El Nino ungrounded water hyacinth plants and allowed for their destruction. Another proposed reason for the hyacinth’s disappearance is the fact that thick cloud cover due to the weather conditions blocked out sunlight, and led to decreased photosynthesis and fertility in established water hyacinth plants (Williams et al. 2007). In early 1998, the latter part of a particularly violent El Nino pattern, water hyacinth populations declined sharply.

Wilson et al. (2007), on the other hand, believes that the ultimate reason for the plant’s disappearance was the introduction of weevils as biocontrol – introducing one species to control another. Although the water hyacinth population did decline sharply in early 1998, plant populations steadied and rose again later that year. They didn’t begin to steadily decline until 1999, 4 years after the introduction of the weevils (Wilson et al. 2007), a typical time period as gathered from other weevil biocontrol situations. Wilson et. al (2007) suggests that El Nino harmed the weevil populations, and that the “new growth was able to proliferate in the absence of weevils”. Weevils were also introduced to other areas – West Africa and Papua New Guinea – and successfully reduced hyacinth populations where they were the only method of control being implemented (Wilson et al. 2007).

To me, it is clear that Wilson et al. (2007) presents a stronger argument. Although Williams et al. (2007) introduces many valid points, Wilson et al. (2007) presents its own evidence and nullifies several parts of Williams’ argument. Despite the fact that I believe Wilson’s argument holds more validity, both documents agree that both El Nino patterns and weevil influence helped decrease water hyacinth populations. As data shows, water hyacinth populations are rising again (NASA 2007). Instead of arguing over who’s more correct, I think the real issue here is to focus on the factors we can control (the weevils) while continuing to search for a more secure solution.

References:

NASA Earth Observatory. 2007. Water Hyacinth Re-invades Lake Victoria. http://earthobservatory.nasa.gov/IOTD/view.php?id=7426. Viewed 20 Jan 2010.

Williams, A. E., R. E. Hecky, and H.C. Duthie. 2007. Water hyacinth decline across Lake Victoria – Was it caused by climatic perturbation or biological control? A reply. Aquatic Botany 87: 94-96.

Wilson, J.R.U., O. Ajuonu, T.D. Center, M. P. Hill, M. H. Julien, F. F. Katagira, P. Neuenschwander, S. W. Njoka, J. Ogwang, R. H. Reeder, and T. Van. 2007. The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp. Aquatic Botany 87: 90-93.